Photoreflectance-difference spectroscopy of GaAs (001) under [110] uniaxial stress: Linear and quadratic electro-optic components
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We report on photoreflectance-difference (PRD) measurements of n-type (001) GaAs crystals under uniaxial stress along [110]. PRD measures the difference between two photoreflectance spectra, one measured with unpolarized light and the other with linearly polarized light along one of the symmetry axis of the crystal. As we have reported previously, the PRD spectrum for the face (001) of cubic crystals comprises only a lineal electro-optic (LEO) component. This is because the quadratic electro-optic component (QEO) for a cubic crystal is isotropic. When a uniaxial stress along [110] is applied, the cubic symmetry is broken leading to an orthorhombic structure. In that case, besides the LEO component, the PRD spectrum comprises a QEO contribution. We show that the overall PRD spectrum can be described by superposing to the LEO line shape previously reported, a quadratic term given by the superposition of the PR line shape and its first energy derivative. The results reported in this work help to develop PRD spectroscopy as a characterization tool of surface electric fields and piezo-optical properties of zinc blende semiconductors.
